Linux grep and regular expressions

grep command

format: grep [-ACINV] [--color=auto] ' Find string ' filename

-A converts binary files to text file

-C calculates the number of ' find string ' found

-I ignores case differences, so case is considered the same

-N Output line number

-V reverse selection, which shows the line without the ' Find string ' content

--color=auto key section plus color display

The basic regular

^: Beginning of the line

$: End of line

Find the beginning of the line with 0:

Find the end of the line with 3:

. Represents a character that must have an arbitrary character

\ escape character, remove the special meaning of special characters

* Repeat 0 to an infinite number of previous characters (be sure to remember is 0 to infinity, if you want grep with ' 3 ' line, with ' * * ' is invalid, should be ' 33* ', in fact grep ' 3 ' = grep ' 33* ')

[List], [ABC] or A or B or c,[0-9] is any of the 0-9 range, similarly [a-z] or [a-z]

[^list] takes a character that is not within that range, and the following example, grep a line that is a whole line of non-lowercase alphabetic characters. * For 0 to an infinite number of meanings, if there is an extended regular expression, with + can express 1 to 1 or more.

\{n,m\} \{n,\} \{\,m}

Extending regular Expressions

Be sure to note that extended regular expressions are written as Egrep

+ Previous * Corresponds to one or more of the previous characters

Egrep ' ^[^a-z]+$ ' = grep ' ^[^a-z][^a-z]*$ '

? 0 or one of the previous characters

| Or

() a set of characters

() + Multiple repeating groups

Identifies the character set, for example, [:d Igit:] instead of [0-9] instance: Egrep-n ' ^ (12|2[[:d igit:]][[:d igit:]]| ( 29|30|31|32) [[:d igit:]][[:d Igit:]] $ ' file*

(Find n,n=12 or 200<=n<=299 or 2900<=n<=3299)

[: Alnum:] Letters and numbers
[: Alpha:] \a Letter
[: Lower:] \l Small Letter
[: Upper:] \u Capital Letter
[: Blank:] white space characters (spaces and tabs)
[: Space:] \s all whitespace (than [: blank:] contains a wide range)
[: Cntrl:] non-printable control characters (backspace, delete, alarm ...) ）
[:d igit:] \d decimal digits
[: xdigit:] \x hex digit
[: Graph:] printable non-whitespace characters
[:p rint:] \p printable character
[:p UNCT:] Punctuation

Finally, grep can fetch characters from multiple files, grep-n ' regular expression ' file1 file2

Linux grep and regular expressions